Fix recursive DekuSize impl (#628)

Author: wcampbell0x2a

deku-derive/src/macros/deku_size.rs

@@ -105,7 +105,7 @@ fn emit_struct(input: &DekuData) -> Result<TokenStream, syn::Error> {
     let DekuDataStruct {
         imp: _,
         wher: _,
-        ident,
+        ident: _,
         fields,
     } = DekuDataStruct::try_from(input)?;
 
@@ -116,6 +116,8 @@ fn emit_struct(input: &DekuData) -> Result<TokenStream, syn::Error> {
     let mut where_clause = where_clause.cloned();
     add_field_bounds(&mut where_clause, fields.iter().copied(), &crate_);
 
+    let ident = &input.ident;
+
     let tokens = quote! {
         impl #imp_generics ::#crate_::DekuSize for #ident #ty_generics #where_clause {
             const SIZE_BITS: usize = #size_calculation;
@@ -132,7 +134,7 @@ fn emit_enum(input: &DekuData) -> Result<TokenStream, syn::Error> {
         imp: _,
         wher: _,
         variants,
-        ident,
+        ident: _,
         id,
         id_type,
         id_args: _,
@@ -165,6 +167,8 @@ fn emit_enum(input: &DekuData) -> Result<TokenStream, syn::Error> {
         add_field_bounds(&mut where_clause, variant.fields.iter(), &crate_);
     }
 
+    let ident = &input.ident;
+
     let tokens = quote! {
         impl #imp_generics ::#crate_::DekuSize for #ident #ty_generics #where_clause {
             const SIZE_BITS: usize = #discriminant_size + #max_variant_size;

tests/test_size.rs

@@ -430,3 +430,18 @@ fn test_enum_with_bits_discriminant_and_data() {
     assert_eq!(SmallDiscriminant::SIZE_BITS, 28);
     assert_eq!(SmallDiscriminant::SIZE_BYTES, None);
 }
+
+#[test]
+fn test_generic_struct_with_deku_size() {
+    #[derive(Debug, DekuRead, DekuWrite, DekuSize)]
+    struct GenericStruct<T>
+    where
+        T: DekuSize + for<'a> DekuReader<'a> + DekuWriter,
+    {
+        value: T,
+    }
+
+    assert_eq!(GenericStruct::<u8>::SIZE_BYTES, Some(1));
+    assert_eq!(GenericStruct::<u16>::SIZE_BYTES, Some(2));
+    assert_eq!(GenericStruct::<u32>::SIZE_BYTES, Some(4));
+}